The technology of the present disclosure relates to an optical scanning device and an image forming apparatus including the same.
Conventionally, there has been known an optical scanning device that is installed in an electrophotographic image forming apparatus, irradiates light beam corresponding to image data to the surface of a photosensitive drum, and scans the light beam in a main scanning direction.
The optical scanning device includes a light source, a rotating polygon mirror that reflects light beam emitted from the light source and deflects and scans the reflected light beam, and an image forming lens that forms an image of the light beam reflected by the rotating polygon mirror on a surface to be scanned.
In the aforementioned optical scanning device, in order to enhance the degree of freedom of an optical path layout, a return mirror may be provided in an optical path from the rotating polygon mirror to the surface to be scanned.
The return mirror has a rectangular column shape long in the main scanning direction. The return mirror is supported from a surface side (a reflection surface side) by four support pins. The return mirror is pushed to the four support pins by a pressing spring. The four support pins abut four corners of the surface of the return mirror.
When the rotating polygon mirror is rotated according to the operation of the optical scanning device, vibration from the rotating polygon mirror is transmitted to the return mirror. As a consequence, bending vibration or rotational vibration is generated in the return mirror.
The bending vibration is vibration by which a center part of the return mirror in the main scanning direction reciprocally displaces in a mirror thickness direction with respect to both end portions of the return mirror. When the bending vibration is generated, density unevenness considerably occurs at a center part of a printed image in the main scanning direction.
On the other hand, the rotational vibration is vibration by which the return mirror alternately displaces in a clockwise direction and a counterclockwise direction when the return mirror is viewed from the main scanning direction. The rotation center of the return mirror is decided by support positions of the return mirror by a plurality of support pins. When the rotational vibration is generated in the return mirror, density unevenness considerably occurs over the whole area of a printed image in the main scanning direction.